The vast majority of knowledge about inorganic periodic mesoporous materials is concerned with oxidic ceramics. See, e.g. Kresge, et al., Nature 359, 710-12 (1992); Zhao, et al., Science 279, 548-52 (1998). A major reason for this seems to be that surfactant templated assembly in aqueous media is very suitable for the preparation of periodic mesoporous oxides, but far less suitable for the synthesis of non-oxidic compounds. The synthesis of non-oxidic mesoporous ceramics usually requires non-aqueous conditions. Therefore, only a few systems are accessible via surfactant templating routes. See, e.g. Maclachlan, et al., Nature 397, 681-84 (1999); Armatas, et al., Science 313, 817-20 (2006); Kamperman, et al., J. Amer. Chem. Soc. 126, 14708-09 (2004); Attard, et al., Microporous Mesoporous Mater. 44-45, 159-63 (2001); Markham, et al., Appl. Phys. Lett. 86, 011912/1-011912/3 (2005).
Unlike the corresponding mesoporous oxides, very little is known about non-oxidic periodic mesoporous ceramics. The stability of a mesoporous framework strongly depends on the framework connectivity and the bond strengths between the constituting elements. Many non-oxidic ceramics like nitrides, carbides, borides, and phosphides have higher framework connectivities than their corresponding oxides because they can make more bonds to their neighbors in comparison to oxygen. For example, C makes four bonds to neighbor atoms in carbides while oxygen makes only two bonds in oxidic ceramics. Furthermore, the bond strengths in non-oxidic ceramics are often nearly as high as in oxides.
In their dense forms, many non-oxidic ceramics exhibit a much greater thermal stability than their corresponding oxides, and the mesoporous forms may therefore have superior thermal properties in comparison with similar oxides. This has been impressively demonstrated in the case of the Si—B—C—N ceramic prepared by Wiesner. See, Kamperman, op cit. However, porous frameworks have a tendency to convert into a more dense form upon heating. Thus, it is desirable to synthesize new mesoporous frameworks, particularly non-oxidic ceramics, with excellent thermal stabilities.
Many non-oxidic ceramics in their dense forms also exhibit much greater hardness and elastic modulus than their corresponding oxides. In fact, the hardest substances known are non-oxidic ceramics (diamond, c-BN, SiC, Si3N4). Increasing the porosity in a material leads inherently to lower mechanical strength, which can dramatically reduce the practical utility of a porous material. A striking example is low dielectric constant materials for microelectronics. The development of new low-dielectric constant materials is one of the most important problems in microelectronics today, yet it is hampered largely by the low elastic modulus of the porous materials available so far. All materials under investigation so far fail to meet the minimum elastic modulus (6 GPa) at porosities necessary to achieve k values of <1.9. See, e.g. Hatton, et al., Mater. Today 9, 22-31 (2006). Furthermore, the elastic modulus is reduced with increasing porosity in any material. Thus, it is desirable to prepare new mesoporous materials with high porosity and high elastic moduli and hardness.